Process for the production of methyl-alkyl tin dichlorides

ABSTRACT

A process for the production of compounds of the formula I 
     
         CH.sub.3 (R)SnCl.sub.2                                     (I) 
    
     wherein R is C 4  -C 20  alkyl, which process comprises reacting dimethyl tin dichloride and R-Cl, wherein R has the above meaning, in the presence of a catalyst of the formula II 
     
         R&#39;(R&#34;).sub.3 M.sup.⊕ X.sup.⊖                   (II) 
    
     wherein R&#39; is C 1  -C 20  alkyl which is unsubstituted or substituted by C 1  -C 4  alkoxy, or is C 7  -C 20  aralkyl, the aryl moiety of which can be substituted by halogen or C 1  -C 4  alkoxy, R&#34; has the same meaning as assigned to R&#39; or is phenyl which is unsubstituted or substituted by C 1  -C 4  alkyl, C 1  -C 4  alkoxy or halogen, M.sup.⊕ is a cation N, P or Sb, and X is an anion selected from the group consisting of chlorine, SnCl 3 , CH 3  -SnCl 4 , (CH 3 ) 2  SnCl 3 , SnCl 5  or SbCl 4 . 
     The compounds of the formula I are intermediates for obtaining stabilizers for halogen-containing thermoplastics.

The present invention relates to a process for the production ofmethyl-alkyl tin dichlorides which are especially useful asintermediates for the manufacture of organo-tin stabilisers forhalogen-containing thermoplastics.

Various syntheses for the production of dialkyl tin dichlorides areknown. For example, U.S. Pat. No. 3,519,665 describes their productionby direct alkylation in the presence of phosphonium iodide as catalyst.However, in order to obtain good yields it is necessary to recycle theby-products to the reaction space.

The production of methyl-alkyl tin dichlorides by transalkylation isknown from U.S. Pat. No. 4,052,427. The reaction ##STR1## wherein R₁ isC₂ -C₂₀ alkyl, proceeds only in the presence of the phosphonium iodidecatalyst referred to above.

The use of iodine-containing catalysts has the disadvantage that itresults in discolouration of the final product, which in turn isdisadvantageous for the later use of this latter as starting materialfor the manufacture of the stabiliser. The object has therefore been toobtain long-chain alkyl tin halides which do not contain iodine.

The production of dimethyl tin dichlorides by direct alkylation, i.e.from tin and methyl chloride in the presence of phosphonium chloride ascatalyst, is described in U.S. Pat. No. 3,901,824. As the reactionresults in a good yield of virtually colourless product, it was obviousto prepare long chain alkyl tin halides also in this manner. However,experiments have shown that the use of phosphonium chloride as catalystleads only to exceedingly poor results. The conclusion to be drawn wasthat phosphonium chloride is unsuitable as catalyst for obtaining alkyltin halides, i.e. even by the method of transalkylation.

Surprisingly, it has now been found that colourless long-chainmethyl-alkyl tin halides additionally containing alkyl tin trichloridesare obtained in good yield by a simple synthesis using phosphoniumchloride as transalkylation catalyst.

Accordingly, the present invention provides a process for the productionof compounds of the formula I

    CH.sub.3 (R)SnCl.sub.2                                     (I)

wherein R is C₄ -C₂₀ alkyl, which process comprises reacting dimethyltin chlorides and R-Cl, wherein R has the above meaning, in the presenceof a catalyst of the formula II

    R'(R").sub.3 M.sup.⊕ X.sup.⊖                   (II)

wherein R' is C₁ -C₂₀ alkyl which is unsubstituted or substituted by C₁-C₄ alkoxy, or is C₇ -C₂₀ aralkyl, the aryl moiety of which can besubstituted by halogen or C₁ -C₄ alkoxy, R" can be identical ordifferent radicals selected from the group R' or is phenyl which isunsubstituted or substituted by C₁ -C₄ alkyl, C₁ -C₄ alkoxy or halogen,M.sup.⊕ is a cation N, P or Sb, and X is an anion selected from thegroup consisting of chlorine, SnCl₃, CH₃ --SnCl₄, (CH₃)₂ SnCl₃, SnCl₅ orSbCl₄.

R as C₄ -C₂₀ alkyl is e.g. n-butyl, t-butyl, n-amyl, iso-amyl,tert-amyl, n-hexyl, 2-ethylhexyl, n-octyl, n-decyl, n-dodecyl,11-methyldodecyl, n-tetradecyl, n-hexadecyl, 16-methylheptadecyl and2-eicosyl. It is preferred that R is a straight chain alkyl radicalcontaining 4 to 12 carbon atoms, such as n-butyl, n-decyl, andespecially n-dodecyl.

R' as C₁ -C₂₀ alkyl which can be substituted by C₁ -C₄ alkoxy is e.g.methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-amyl, n-octyl,n-dodecyl, 11-methyldodecyl, n-tetradecyl, 16-methylheptadecyl,nonadecyl, 2-ethoxyethyl, 4-ethoxybutyl. It is preferred that R' is astraight-chain C₁ -C₄ alkyl radical, such as methyl, ethyl, n-propyl orespecially n-butyl.

R' as C₇ -C₂₀ aralkyl is e.g. benzyl or 1-phenylethyl, and if the arylmoiety is substituted by halogen or C₁ -C₄ alkoxy can be e.g.2-methoxybenzyl, 2-methoxyphenylethyl, 3-chlorobenzyl. The preferredidentity of R' is benzyl.

R" can have the same meaning as R' or can be phenyl, 3-methoxy-phenyl,tolyl, xylyl or 4-chlorophenyl. It is preferred that R" is phenyl,benzyl or n-butyl. The most preferred identity of R" is n-butyl.

M.sup.⊖ is N, P and Sb, preferably P. X is a chlorine-containing anion,e.g. chlorine, SnCl₃, CH₃ --SnCl₄, (CH₃)₂ S_(n) Cl₃, SnCl₅ or SbCl₄. Itis preferred that X is SnCl₅.

The most preferred catalyst is tributylmethylphosphoniumpentachlorostannate (IV).

Examples of compounds of formula I are:

methyl-n-butyl tin dichloride

methyl-n-hexyl tin dichloride

methyl-n-decyl tin dichloride

methyl-n-dodecyl tin dichloride

methyl-iso-tridecyl tin dichloride

methyl-n-tetradecyl tin dichloride.

In the process of the invention, the molar ratio of dimethyl tindichloride to R--Cl is usually about 1:1. It is preferred to use a smallexcess of R--Cl.

The reaction can be carried out in the temperature range from 160° to240° C., with the preferred range being from 180° to 200° C. Thereaction medium can also contain customary inert solvents, e.g.aliphatic and aromatic hydrocarbons, ethers, esters, cyclic carbonates,sulfoxides or sulfolanes. However, the preferred solvents are (CH₃)₂SnCl₂ or R--Cl.

The catalyst can be employed in amounts of 5 to 50 mol. %, based on(CH₃)₂ SnCl₂. The preferred amount is 10 to 30 mol. %.

The starting dimethyl tin dichloride and the onium chloride catalyst canbe obtained in known manner as described in U.S. Pat. No. 3,901,824. Thecompounds R--Cl are known or they can be obtained by methods commonlyknown in the art.

The compounds of the formula I are important intermediates for themanufacture of organo-tin stabilisers which are used forhalogen-containing thermoplastics, such as PVC. Such manufactureincludes the reaction of organic fatty acids containing 6 to 18 carbonatoms with alkylthiols, mercapto esters or alcohols, as described e.g.in Canadian patent specification No. 595,138.

The compounds of the formula I produced by the process of this inventionis obtained as a mixture with R--SnCl₃ and CH₃ SnCl₃, wherein R is C₄-C₂₀ alkyl.

The reaction mixture can be used direct for further processing to give astabiliser. The content of alkyl tin trichloride, which is onlyobtainable with difficulty by conventional methods, acts as synergist inthe stabiliser.

The process of the present invention results in surprisingly goodyields. A great advantage of the onium catalysts employed is that theydo not lead to any discolouration of the products. Aside from thisadvantage, they are also cheaper than iodine-containing catalysts. Thehigh yield is obtained without recycling the by-products to the reactionspace. A further advantage compared with the process using phosphoniumiodide catalysts is that alkyl tin trichloride is obtained. Thiscompounds acts as synergist in a stabiliser produced direct from thereaction mixture.

The invention is illustrated in more detail by the following Example, inwhich percentages are by weight.

EXAMPLE

A three-necked flask equipped with stirrer and reflux cooler is chargedat 180° C. with 0.2 mole of (CH₃)₂ SnCl₂ and 0.05 mole of catalyst. Then0.4 mole of lauryl chloride is slowly added over the course of 4 hourswhile gradually raising the temperature to 200° C. Stirring is thencontinued for a further 2 hours at 200° C.

When the elimination of methyl chloride is complete, the resultantmixture has the following composition (analysis by gas chromatography):

    __________________________________________________________________________                  ##STR2##                                                        Catalyst     (comparison)    [CH.sub.3 (CH.sub.2).sub.3 ].sub. 3P.sup..sym                                 .CH.sub.3 SnCl.sub.5.sup.⊖               __________________________________________________________________________                                 3                                                (CH.sub.3).sub.2 SnCl.sub.2 -reaction                                                      87.1            93.7                                             in %                                                                          Sn-distribution in %                                                                       12.9            6.3                                              (CH.sub.3).sub.2 SnCl.sub.2                                                   CH.sub.3 [CH.sub.3 (CH.sub.2).sub.11 ]SnCl.sub.2                                           81.6            63.5                                             CH.sub.3 SnCl.sub.3                                                                        5.5             12.1                                             CH.sub.3 (CH.sub.2).sub.11 SnCl.sub.3                                                      --              18.1                                             __________________________________________________________________________

CH₃ [CH₃ (CH₂)₁₁ --SnCl₂ can be separated as main component bydistillation. Melting point: 43°-45° C.

What is claimed is:
 1. A process for the production of a compound of theformula I

    CH.sub.3 (R)SnCl.sub.2                                     (I)

wherein R is C₄ -C₂₀ alkyl, which process comprises reacting dimethyltin dichloride and R--Cl, wherein R has the above meaning, in thepresence of a catalyst of the formula II

    R'(R").sub.3 M.sup.⊕ X.sup.⊖                   (II)

wherein R' is C₁ -C₂₀ alkyl which is unsubstituted or substituted by C₁-C₄ alkoxy, or is C₇ -C₂₀ aralkyl, the aryl moiety of which can besubstituted by halogen or C₁ -C₄ alkoxy, R" can be identical ordifferent radicals selected from the group R' or is phenyl which isunsubstituted or substituted by C₁ -C₄ alkyl, C₁ -C₄ alkoxy or halogen,M.sup.⊕ is a cation N, P or Sb, and X is an anion selected from thegroup consisting of CH₃ --SnCl₄, (CH₃)₂ SnCl₃, SnCl₅ or SbCl₄.
 2. Aprocess according to claim 1 for the production of a compound of theformula I in admixture with R--SnCl₃ and CH₃ SnCl₃, wherein R is asdefined in claim
 1. 3. A process according to claim 1, wherein R isstraight chain C₄ -C₁₂ alkyl.
 4. A process according to claim 1, whereinR' and R" are C₁ -C₂₀ alkyl.
 5. A process according to claim 1, whereinR' and R" are straight chain C₁ -C₄ alkyl.
 6. A process according toclaim 1, wherein M.sup.⊕ is P.
 7. A process according to claim 1 for theproduction of methyl-n-dodecyl tin dichloride.
 8. A process according toclaim 1, wherein the catalyst is tributylmethylphosphoniumpentachlorostannate (IV).
 9. A process according to claim 1, wherein thereaction is carried out in the temperature range from 160° to 240° C.10. A process according to claim 1, wherein the reaction is carried outin the presence of an inert solvent.
 11. A process according to claim10, wherein the solvent is (CH₃)₂ SnCl₂ or R--Cl, wherein R is asdefined in claim
 1. 12. A process according to claim 1, wherein thecatalyst is used in an amount from 5 to 50 mol. %, based on the dimethyltin dichloride employed.